List集合去重方法

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已于 2023-05-11 15:24:19 修改

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分类专栏：工作学习文章标签： java jvm servlet

于 2023-04-24 09:58:19 首次发布

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文章展示了如何使用Java8的StreamAPI对List<String>和List<实体类>进行去重操作。对于List<Object>中特定属性的去重，文章提供了创建TreeSet并结合Comparator的方法，确保根据对象的treeId和treeContentId属性实现去重。

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1.List<String> 去重

list.stream().distinct().collect(Collectors.toList());

去重前：AABBC
去重后：ABC

2.List<实体类>去重

List.stream().distinct().collect(Collectors.toList())

去重前：[{"stuNo":"001","name":"Tom"},{"stuNo":"002","name":"Mike"},{"stuNo":"001","name":"Tom"}]
去重后：[{"stuNo":"001","name":"Tom"},{"stuNo":"002","name":"Mike"}]

3.`List<Object>` 中 `Object` 某个属性去重

方法：

xxxxList.stream().collect(
            Collectors.collectingAndThen(Collectors.toCollection(
                    () -> new TreeSet<>(Comparator.comparing(o -> o.getTreeId() + ";" + o.getTreeContentId()))),
                ArrayList::new))

xxxxList.stream().collect(
            Collectors.collectingAndThen(Collectors.toCollection(
                    () -> new TreeSet<>(Comparator.comparing(o -> o.getTreeId() + ";" + o.getTreeContentId()))),
                ArrayList::new))

package org.example;

public class StoryColumn {
    private String treeId;

    private String treeContentId;

    public String getTreeId() {
        return treeId;
    }

    public void setTreeId(String treeId) {
        this.treeId = treeId;
    }

    public String getTreeContentId() {
        return treeContentId;
    }

    public void setTreeContentId(String treeContentId) {
        this.treeContentId = treeContentId;
    }
}

package org.example;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.TreeSet;
import java.util.stream.Collectors;

public class testList {
    public static void main(String[] args) {
        StoryColumn storyColumn1 = new StoryColumn();
        storyColumn1.setTreeId("1161");
        storyColumn1.setTreeContentId("1042551");
        StoryColumn storyColumn2 = new StoryColumn();
        storyColumn2.setTreeId("1161");
        storyColumn2.setTreeContentId("1042551");
        StoryColumn storyColumn3 = new StoryColumn();
        storyColumn3.setTreeId("1160");
        storyColumn3.setTreeContentId("1042550");
        StoryColumn storyColumn4 = new StoryColumn();
        storyColumn4.setTreeId("1160");
        storyColumn4.setTreeContentId("1042550");
        StoryColumn storyColumn5 = new StoryColumn();
        storyColumn5.setTreeId("1165");
        storyColumn5.setTreeContentId("1042555");

        List<StoryColumn> storyColumnList = new ArrayList<>();
        storyColumnList.add(storyColumn1);
        storyColumnList.add(storyColumn2);
        storyColumnList.add(storyColumn3);
        storyColumnList.add(storyColumn4);
        storyColumnList.add(storyColumn5);

        for (StoryColumn storyColumn : storyColumnList) {
            System.out.println(storyColumn.getTreeId()+"----"+storyColumn.getTreeContentId());
        }

        storyColumnList = storyColumnList.stream().collect(
            Collectors.collectingAndThen(Collectors.toCollection(
                    () -> new TreeSet<>(Comparator.comparing(o -> o.getTreeId() + ";" + o.getTreeContentId()))),
                ArrayList::new));

        System.out.println("-------------------------------");

        for (StoryColumn storyColumn : storyColumnList) {
            System.out.println(storyColumn.getTreeId()+"----"+storyColumn.getTreeContentId());
        }

    }
}

运行：

1161----1042551
1161----1042551
1160----1042550
1160----1042550
1165----1042555
-------------------------------
1160----1042550
1161----1042551
1165----1042555